EVERETT, Wash. — Authorities arrested a Washington state student suspected in a school shooting plot after his grandmother showed officers plans for an attack.

Police in Everett, which is about 30 miles north of Seattle, arrested 18-year-old Joshua Alexander O'Connor on attempted murder and other charges at ACES High School on Tuesday, The Daily Herald reported.

Earlier, O'Connor's grandmother called 911 and showed responding officers a journal where he allegedly drew up plans to shoot students and use homemade explosives at the school, police said.

O'Connor wrote that he wanted the death count to be as high as possible so that the shooting would be infamous, according to court papers. His entries included details about making pressure-cooker bombs, activating inert grenades and deploying explosives for maximum casualties, court papers said.

Detectives serving a search warrant at the grandmother's house seized the student's journal, a rifle found inside a guitar case and inert grenades.

Public defender Rachel Forde noted the gun and the grenade shells were legal to possess. She said the "musings and ventings" in O'Connor's journal weren't enough evidence to support a charge of attempted murder.

Another entry allegedly described an armed robbery of a convenience store that police believe O'Connor participated in Monday night.